Allows for remote connections on same network (as Jekyll now seems to default to 127.0.0.1 which means it does not react to incoming external requests)

* use a trailing slash when possible
* use https when possible
* remove a few redirected links
* consistently use `https://popper.js.org/`
* fix `iconUrl` in nuget files
* change Jekyll Windows guide to the official one

* ignore `twbsconfig.yml`
* add a trailing slash for folders